The invention relates to a method and apparatus in which a mould cavity is evacuated prior to the introduction of a fluid settable material. As used in this specification the term fluid will be understood to refer to any material in a state such that it can flow, and in particular will include not only liquid but also paste-like materials. Further, the term "settable" will be understood to refer to any fluid material capable of becoming solid after the elapse of time, regardless of the physical phenomenon which results in solidification, and will include hardening upon heating or cooling, curing by chemical or other means and any other solidification process which will result in a fluid material a hereinbefore defined becoming solid.
Prior art apparatus for moulding articles in an evacuated cavity is typified by the mould described in UK Patent 1,432,333 which comprises a male and female mould part shaped to be assembled to define a cavity, a seal for sealing the cavity against the atmosphere, and an aperture in one of the mould parts for the application of a vacuum to the cavity, the mould parts and the seal being arranged to permit drawing of the mould parts together with relative movement thereof at the seal. The use of an internal vacuum to draw the male and female mould parts together is stated in that Patent to have the advantage that the only pressure to which the mould is subject is atmospheric pressure acting uniformly over the whole mould surface to squeeze the moulding material into the empty parts of the cavity during the closing down of the mould so that the mould parts need only be sufficiently robust to avoid distortion under these conditions.
It is considered, however, that the satisfactory production of injection moulded items, particularly if resin is used as the flowable material, requires more than the mere evacuation of the mould cavity to ensure a complete filling of the mould and avoidance of cavitation bubbles in the material before setting so that components of accurate dimensions, complete form and homogeneous structure are reliably produced upon each moulding operation.